The 23-year-old clocked an impressive 54.58 seconds to win in Monday's heats of the 100m freestyle at the Queensland Championships.

She then went quicker (53.80) in the night's final, finishing second behind Mollie O'Callaghan (53.62) in a statement performance ahead of next year's world championships and Commonwealth Games.

Subdued until that point, the small crowd in the stands gave Jack a warm applause in a gesture that was gratefully received.

"It was so nice to know that people that I have potentially never met are passionate about seeing me back," she said.

"It boosts my confidence; I honestly did have fears that not everyone would be happy to see me back and that's something I had to overcome. I couldn't stop smiling."

Coach Dean Boxall was thrilled with his charge's return, saying she had every chance to be a force at the Paris 2024 Games.

""This is really exciting, Shayna's talented. It was going to be about where her mind was," he said.

"But she's mentally tough, (to get through) what she's been through."

Jack was initially banned for four years after testing positive to Ligandrol on June 26, 2019, almost three weeks before the world championships in South Korea.

The Queenslander appealed her ban to the Court of Arbitration for Sport (CAS) which reduced her suspension to two years, finding Jack did not knowingly ingest the substance.

Sport Integrity Australia (SIA) appealed that reduction, citing a need for clarity regarding anti-doping legal principles.

CAS rejected the SIA appeal last September, allowing Jack to return to the sport.

"The toughest part for me was when they did appeal that second time, I didn't have the money to afford it," she said.

"So it was really amazing to see how many people got behind me ... I'm standing here racing because of them.

"There were lots of nerves this morning knowing I'd be on the blocks alone in a way (after swimming in a relay team on Saturday).

"It took a long time to get back here and I'm really proud am I here."

CAS, in its full decision published in November last year, noted Jack said she didn't know how the substance was in her system but suggested three possible sources for her positive test.

Jack proposed supplements she took could have been contaminated at manufacturing.

Another possibility was the supplements were contaminated by being prepared or mixed in a blender that may have been contaminated or contained Ligandrol.

A third possibility was Jack may have come into contact with the Ligandrol or ingested it as a result of using a pool and/or gym open to the public in Townsville or Cairns while training before the 2019 world championships.

Australian Associated Press